2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/51951This paper completes the work, initiated in [hep-th/9906003,hep-th/0301204], further referred as Parts I and II, concerning to Dirac's quantization of Nambu-Goto theory of open string, formulated in the space-time of dimension d=4. Here we perform more detailed study of Gribov's copies in the classical mechanics and determine the quantum spectrum of masses for the arbitrary spin case.High Energy Physics - Theorytext